第一节从方框中选出最佳选项完成下面的对话。

A: Hi, Bill. You were not at school yesterday.     小题1:

B: Oh, I fell off my bike on my way to school and hurt my leg.

A: I’m sorry to hear that.     小题2:

B: No, my father took me to the hospital.     小题3:

A: We should be more careful when we ride. In fact, we should never ride too fast.

B: You are right.     小题4:    If we break the rules, we may be in danger.

A: Let’s go to the traffic station to learn more rules.

B:     小题5:

在计算代数式（2x³-3x²y-2xy²）-（x³-2xy²+y³）+（-x³+3x²y-y³）的值，其中x=0.5，y=-1时，甲同学把x=0.5错抄成x=-0.5，但他计算的结果是正确的。试说明理由，并求出这个结果。